X-ray tube



Dec. 14, 1943. z J LE 2,336,769

X-RAY TUBE Filed March 26, 1942 INVENTORI" Zed dmze B g; CpW

Patented Dec. 14, 1943 X-RAY TUBE Zed J. Atlee, Elmhurst, 111., assignor to General Electric X-Ray Corporation, Chicago, 111., a corporation oi New York Application March 26. 1942, Serial No. 436,291

Claims. (Cl. 250148) My invention relates in general to lectronics and has more particular reference to the provision of an improved X-ray generator.

An important object of the present invention a is to provide an X-ray generator having a metallic envelope structure substantially immune to deterioration as a result of X-ray action on the envelope; a further object being to form the envelope principally of metal, particularly in the zones or areas thereof which are exposed to the direct action of X-rays when the device is in operation.

Another important object is to provide an envelope construction utilizing preferably metallic material at the zones or areas wher exposed to the deleterious efiects of X-rays and electronic impact and to provide means in which the absorption of useful X-rays by the envelope is reduced to an inconsequential minimum.

A further object is to provide an X-ray tube embodying a rotating anode and having a metallic envelope, and consequently adapted for high voltage operation, in which difficulties due to etching and localized heating of the envelope, which are accentuated in tubes embodying envelopes of glass, are eliminated in metal envelope tubes embodying my present invention; a further object being to utilize a preferably seamless steel tube within which all of the elements of the generator, including glass end seals, are enclosed, so that by grounding the steel tube, the entire device may be rendered absolutely shock-proof, and by thus maintaining the metal portions of the envelope at ground potential, substantially all of the dimculties encountered in glass envelopes are eliminated.

A further object is to provide an X-ray generator having a metal envelope and glass end seals, wherein the active elements of the generator are arranged within the metallic envelope portion in a manner such that the glass end seals are entirely shielded and protected against metallic deposit through evaporation of the electrodes during the life of the tube, the'end seals, furthermore, being shielded and protected against direct X-ray action.

Another important object is to provide an X- ray generator in which the anode and cathode electrodes are supported in place within a metallic envelope section on glass end seals, the structure being arranged to apply minimum mechanical load on the end seals.

Another important object is to provide an X- ray generator embodying a cathode and a rotating anode enclosed within a metallic envelope, and

to provide for driving the anode by means of a motor mounted outwardly of the envelope acting upon the anode through the metallic envelope walls of the generator; a further object being to utilize pole pieces set in the walls of the metallic envelope in a fashion magnetically insulated from the envelope opposite the anode to deliver driving torque thereon through said pole pieces from magneto motive means disposed outwardly of the envelope; a further object being to set the pole pieces in the envelope without impairing the vacuum conditions necessarily maintained within the envelope for the satisfactory operation of the device as an X-ray generator.

Among the numerous other important objects and advantages of the invention is to provide an extremely simple and inexpensive X-ray generator adapted for mass production methods and embodying a substantially all-metal construction having the advantage of manufacturing accuracy inherent to metal parts produced by machine tools.

These and numerous other important objects, advantages, and inherent functions of the invention will be fully understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing:

Figure 1 is a sectional view illustrating an X- ray generator embodying the features of my pres-' ent invention; and

Figures2 and 3 are sectional views taken, respectively, along the lines 2-2 and 33 in Figure 1.

To illustrate the invention, I have shown on the drawing an X-ray tube ll comprising an anode l3 and a co-opei'ating cathode l5 enclosed in a sealedenvelope comprising a seamless steel tube H.

The anode I3 comprises a rotary anode element providing a target IS in. position opposite the cathode to receive the impingement of electrons emitted by the cathode during the operat on of the device as an X-ray generator. The anode may be formed and arranged and turnably supported upon a stem 2! in the manner taught in my co-pending application, Serial No. 39u,3z2, flied April 25, 1941, upon which Letters Patent No. 2,311,725 issued February 23, 1943. The stem 2| forms an annular seat 23 on which is sealed a mounting disk 25 which, in turn, is supported on the tube ii in position carrying the anode I3 within one end of the tube, the cathode being similarly supported in the other end of the tube electron emissionfilament 20 in position to emit electrons in the direction of the target l9 when energized. The filament, at its opposed ends, is mounted on, electrically connected to, and supported by conductor stems 22 which extend through openings in the head I6 and are mounted.

in insulating brackets behind the head. The stems are electrically connected with conductors 24 which pass through openings in a mounting disk or plate 25 forming a part of the cathode structure. These openings are fitted with grommets 28 in which the conductors 24 are secured. The cathode head i6 is supported on the plate 23 by means forming a tubular skirt 30, which is secured to the head l6 and the plate 26, as by means of fastening screws 34, whereby the head and plate are maintained in spaced relationship by the skirt means 30, which also serves to enclose a space or chamber 3| between the head and the plate.

The anode and cathode structures are respectively supported in the opposed ends of the tube l1 by similar mountings carrying the heads 25 and 26, respectively. To this end, the heads 25 and 26 are each formed with an annular marginal groove. An annular sealing member 33 is sealingly secured at one end thereof in said groove, as by soldering, welding or brazing, the other end of the element 33 being formed with a tapered annular edge which makes a glass-tometal seal 35 with one end of a glass sleeve 31. The anode and cathode structures are supported at the opposite ends of the tubular metal sleeve H on mountings comprising the preferably metallic end rings 39, the marginal edges of which are sealed in hermetic fashion, as at 4|, by sol dering, welding or brazing, to the opposite ends of the tube IT. The rings 39 each carry a preferably metallic sleeve member 43 sealed, as by soldering, brazing or welding, in an annular seat formed on the ring 39. The members 43 have tapered edges which form annular glass-to-metal seals 45, respectively, with the outer ends of the glass anode and cathode mounting sleeves 31. The seal elements 33 and 43 preferably comprise metal having a relatively high proportion of nickel, said elements preferably comprising Fernico containing nickel in quantities of the order of 40%, whereby to facilitate the.making of the annular glass-to-metal seals 35 and 45. The anode skirt 21 and the cathode skirt 30 extend in position enclosing the seals 35.and a substantial portion of the glass sleeves 31, the anode skirt enclosing a chamber 32 adjacent the anode mount ing disk 25.

It will be seen also that the anode and cathode structures may be formed and completed as subassembly units on their respective mountings,

comprising the end ring 39, the insulating sleeve 31, and the metal-to-glass sealing members 33 and 43, prior to the mounting of the anode and cathode in the envelope tube i1.

be accomplished as a final assembly operation merely by sealing the end rings 33 in place in the opposite ends of the tube l1.

It should be understood, of course, that an X- ray generator functions to produce X-rays as a result of the impingement on the anode target I9 of electrons emitted by the cathode filament 20. For efilcient operation of the device as an X-ray generator, the atmosphere within the envelope is preferably maintained under substantial vacuum conditions. This may ordinarily be accomplished by first thoroughly evacuating the envelope as a part of the manufacturing process, the evacuation being accomplished when the anode and cathode sub-assemblies are finally assembled and sealed in the envelope, said final as- I sembly and sealing operation being preferably The assembly and sealing of the anode and cathode may then accomplished as a vacuum furnace. Evacuation of the envelope may also be accomplished after sealing the anode and cathode in the tube H by attaching the same to suitable exhaust means, as by a connection formed through the cathode support sleeve 31. During evacuation, the device and all of its operating parts are strongly heated in order to remove all impurities, including such gases as may be occluded in the anode, cathode and envelope walls. After the device has thus been exhausted to the greatest possible extent, as a final operation to remove all remaining impurities, a gettering operation may be performed within the envelope.

By making the envelope of metal, in accordance with my present invention, the fabrication of the generator is simplified considerably, since the envelope may be evacuated merely by placing the assembled device in a vacuum chamber prior to the formation of the end seals 4|, the rings 39 with anode and cathode structures mounted thereon being merely mechanically supported in place at the ends of the sleeve l1. Then, after the envelope has been exhausted to a desired degree in the furnace, the seals 4| may be formed in the vacuum chamber as by suitable induction heating means.

The final gettering operation may be accomplished by vaporizing a suitable gettering material, such as barium, within the envelope. By vaporizing barium within the evacuated envelope, all remaining impurities may be caused to unite with the barium vapor to form innocuous solid gettering end products which, upon condensation,

will become deposited within the envelope. The gettering operation may be accomplished within the cathode chamber 3|, or may be accom plished within the chamber 32 in the anode, or in both the anode and cathode, since I prefer to evaporate barium in the anode to lubricate the bearings thereof in the manner taught in my aforesaid co-pending application, Serial No. 390,322, filed April 25, 1941, upon which Letters Patent No. 2,311,725 issued February 23, 1943.

By arranging the anode and cathode structures as shown and evaporating a suitable gettering material within the chambers 3| or 32, or both, gettering end products will be deposited upon the internal surfaces of the gettering chambers and will thus be prevented from-becoming deposited upon the active portions of the anode and cathode. The gettering material may be supported within the chambers 3| and 32 and evaporated therein by any suitable or preferred means. Preferably, however, the gettering material is supported in the chamber 3| by a carrier wire 5| electrically connected at one end on the,plate 2B and at the other end on a conductor 53, the carrier wire 5| having portions intermediate the ends thereof arranged in loops within the chamber 3|. The conductor 53 extends through an opening in the plate 26 and is sealed in a grommet 55. In the anode chamassaveo site ends toconductors it which extend through openings in the plate 25. the conductors bein sealed in grommets 56. I

The carriers BI and '52 each preferably comprisehollow conductor means enclosing the gettering material and having weakened wall portions. By passing electrical current through the hollow conductors i and", as,by connecting a suitable electrical power source between the conductors 54, or between the conductor 53 and a stem 51 mounted on and electrically connected to the plate 26 and extending thence preferably centrally within the glass sleeve 31, the carriers II and 52 may be heated within the envelope to thereby vaporize the gettering material carried therein. The vaporized material so produced will be projected outwardly of the carriers through the weakened wall portions thereof to perform a gettering operation within the chambers 3i and 32, resulting end products being deposited upon the inner walls of the chambers.

While any suitable cathode structure may be employed; I prefer to utilize a cathode embodying a thoriated filament and to include, in the cathode structure, means for measuring vacuum conditions within the envelope in the manner taught in my co-pending application, Serial No. 422,530, filed December 11, 1941.

The steel envelope I1 is preferably formed with awlndow opening 58 opposite the target l8, and a pane of material 6|, substantally transparent to X-rays, may be sealed on the envelope at said opening. I prefer to utilize a beryllium window-pane 6i, since beryllium has an exceedingly low X-ray absorbing characteristic. The beryllium pane may be applied by soldering it in a ring 63 of Monel metal by means of a brazing alloy which may comprise equal parts of silver and copper. The soldering or brazing operation may be accomplished in a hydrogen furnace with calcium chloride or other halogen salt as,a flux. The copper-silver alloy has the property of wetting the beryllium but does not go fully into solution therewith before a satisfactory hermetic joint is formed. In order that the alloy may flow evenly and freely'upon the beryllium member to form the Joint, it should be in a highly molten state; but the higher the temperature, the faster is the rate at which beryllium will go into solution. Pure copper in the molten state rapidly dissolves beryllium, but pure silver, on the other hand, dissolves beryllium slowly. The alloy comprising equal parts of copper and silver, or containing a preponderance of silver up to about 66%, has an intermediate rate of solution with beryllium and is satisfactory for the purpose of sealing the beryllium disk in its supporting ring 63. Gold also may improve the sealing effect if present in the soldering alloy in quantities between 10% and 30%.

For the purpose of sealing the ring 63 upon the envelope sleeve I1, I prefer to utilize the eutectic alloy of silver and copper comprising substantially 72% silver and 28% copper.

In order to rotate the anode It, the stator 65 ,of an induction motor may be mounted around sleeve l1, said openings being sealed around the pole pieces to preserve the vacuum-tight condition of the envelope. The pole pieces 81 are disks of iron or other magnetic material and are magnetically insulated from the steel sleeve I! by annular collars 63 of copper, the pole pieces being annularly sealed in hermetic fashion, as at H, in the copper collars, the seals being accomplished by brazing preferably with pure silver as a brazing material. The copper collars, in turn,

are annularly sealed, as at 13, in the openings formed in the sleeve H, the seals I3 being accomplished by soldering the collars to the sleeve by means of a eutectic silver alloy comprising approximately .72% silver and 28% copper.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. A device of the class described comprising a tubular metallic member forming a sealed and evacuated envelope, opposed electrodes in the envelope, insulated support means for mounting said electrodes, one of the electrodes being tumably mounted on said insulated support means, and pole pieces carried by said tubular member in position opposed to said turnably mounted electrode, and motor means disposed outwardly of said envelope and having magneto motive relationship with said turnably mounted electrode.

2. A device of the class described comprising a tubular metallic member forming a sealed and evacuated envelope, opposed electrodes in the envelope, insulated support means for mounting said electrodes, one of the electrodes being turnably mounted on said insulated support means, and pole pieces carried by said tubular member opposite said turnably mounted electrode, whereby motor means disposed outwardly of the envelope may have magnetic motive relationship for rotating the turnably mounted electrode within the envelope.

3. A device as set forth in claim 2, wherein said pole pieces are magnetically insulated from said tubular member.

- 4. A device as set forth in claim 2, wherein said pole pieces comprise disks of iron, and copper mounting rings in which said pole pieces are hermetically sealed. said mounting rings being sealed in openings formed in the tubular member opposite the turnably mounted electrode.

5. A device as set forth in claim 2, wherein said pole pieces comprise disks of iron, and copper mounting rings in which said pole pieces are hermetically sealed, said mounting rings being sealed in openings formed in the tubular member opposite the turnably mounted electrode, said pole pieces being sealed in said rings and said rings being sealed to said tubular member by fastening material comprising silver.

6. A device of the class described comprising a tubular metallic member forming a sealed and evacuated envelope, opposed electrodes therein, insulated support means carried by said envelope for supporting said electrodes, said insulated support means comprising glass members sealed to the tubular member in spaced relationship and forming mountings for said electrodes, including a mounting turnably supporting one of said electrodes within said tubular member, motor means disposed outwardly of said envelope and having magneto motive relationship with said turnably supported electrode, and pole pieces carried by said tubular member in a position opposed to the turnably supported electrode.

7. A device as set forth in claim 6, wherein said electrodes each comprise skirt portions formed to shield the insulating member on which mounted from direct impingement of rays emanating from the other electrode.

8. A device as set forth in claim 6, wherein each electrode includes a metal sealing portion forming an annular edge making a glass-to-metal seal with the glass mounting member on which the electrode is supported, and wherein each electrode comprises a skirt portion embracing its corresponding glass-to-metal seal.

9. A device as set forth in claim 6, wherein said glass support members comprise sleeve-like elements, each carrying an electrode sealed thereon and each, in turn, sealed to the tubular metallic envelope member whereby said glass members form pockets within the envelope and opening, at the opposite ends thereof for the circulation oi cooling fluid in heat exchange relationship with the electrodes.

10. A device of the class described comprising a tubular metallic member forming a sealed and evacuated envelope, an electrode mounting forming an end seal extending at and within each of the opposed ends of the tubular metallic member, an electrode on each of said mountings, at least one of said electrodes being turnably supported on its mounting, said mountings each comprising an annular glass sealing and supporting member and each electrode having a skirt portion embracing the glass member or its mounting whereby to shield the same from rays generated in said envelope, and pole pieces carried by said tubular member opposite said tumably mounted electrode whereby motor means disposed outwardly of the envelope may have magneto motive relationship for rotating the turnably mounted electrode within the envelope.

ZED J. ATLEE. 

